<html>
  <head>
    <title>flex学习</title>
    <meta charset="utf8" />
    <style>
      body{
        flex-direction: column;
        height: 100%;
        display: flex;
        margin: 0px;
      }
      .upper {
        display: flex;
        height: 200px;
      }
      .first {
        background-color:aqua;
        width: 100px;
      }
      .second {
        background-color: aquamarine;
        flex: 1;
      }
      .lower {
        display: flex;
        flex: 1;
      }
      .third {
        background-color: blueviolet;
        width: 100px;
      }
      .fourth {
        background-color: burlywood;
        flex: 1;
      }
    </style>
  </head>
  <body>
    <div class="upper">
      <div class="first">第一个</div>
      <div class="second">第二个</div>
    </div>
    <div class="lower">
      <div class="third">第三个</div>
      <div class="fourth">第四个</div>
    </div>
  </body>
</html>